Galaxy S21 battery health and charging
How big each Galaxy S21 battery is, how to check its health, what’s normal for a phone released in 2021, and what to do when it won’t charge. Useful whether you own one or are about to buy one used.
Battery capacity of each model
| Model | Battery | Launch price (US) |
|---|---|---|
| Galaxy S21 | 4,000 mAh | $799 |
| Galaxy S21+ | 4,800 mAh | $999 |
| Galaxy S21 Ultra | 5,000 mAh | $1199 |
Charging: USB-C, 25 W Super Fast Charging. Wireless: Fast Wireless Charging 2.0 (up to 15 W), Wireless PowerShare.
Updates: Samsung’s promised updates have ended: no more Android versions, and regular security updates have stopped.
How to check Galaxy S21 battery health
- Open the Samsung Members app › Support › Phone diagnostics › Battery status. It rates the battery Good, Normal or Bad and shows its life.
- Dial *#0228# on many Samsung models for a battery status screen with the voltage and temperature.
- Look at Settings › Battery for “Protect battery”: if it is on, charging stops at 85% by design.
What to know about the Galaxy S21 battery
- Without security updates, banking apps may stop working on it over time. Fine as a spare or for a child; think twice as a main phone.
- Check battery health in the Samsung Members app › Support › Phone diagnostics › Battery status.
- The S21 and S21+ use Exynos chips in many countries, which run warm and drain faster than Snapdragon models.
Galaxy S21 won’t charge: what to try
- Try another USB-C cable and charger you know work. A damaged cable is the most common cause.
- Clean the port. USB-C ports fill with pocket lint that stops the plug seating fully; ease it out with a wooden toothpick, never metal.
- Restart the phone. A software glitch can stop charging until the next restart.
- If it says “Moisture detected”, dry the port and wait; wireless charging still works meanwhile. If it stops at 85%, “Protect battery” is on.
- Try wireless charging, if the model supports it. If wireless works and cable doesn’t, the port or its flex cable is the problem, not the battery.
- If it drops from 20–30% to off, or shows a sudden jump in percentage, the battery is worn and needs replacing.
Still not charging? Open mxmob.com/check and run the charging test: it shows the instant the phone sees power, so you can tell a dead port from a dead battery. Our battery test shows the charge level, charging state and estimated time to full.
Buying a used Galaxy S21?
Ask the seller for a screenshot of the battery health screen before you travel. When you meet, run the free hardware test on the phone itself, check the IMEI with our IMEI checker, and see our price checker to know what a fair price is. A battery under 85% is a reason to ask for less, not always a reason to walk away.
FAQ
What battery health is normal for a used Galaxy S21?
Most batteries lose roughly 4–8% of capacity a year with daily use. Above 85% is fine; 80–85% needs a battery within a year; under 80% means a new battery now.
How much does a new Galaxy S21 battery cost?
An official replacement from Samsung or an authorised shop usually costs $70–$120 in the US; third-party shops are cheaper but may use lower-quality cells. Subtract that from your offer if health is under 85%.
Can I test the Galaxy S21 battery and charging before I buy?
Yes. Open mxmob.com/check on the phone and run the charging test: plug the cable in and out and the page confirms it sees power. Run it with the phone’s screen on for ten minutes and watch the percentage.